Joint frontrunner for the Republican nomination, Mitt Romney, has bowed to pressure from rival candidates and disclosed his income tax records.

They reveal that he had a joint income with his wife, Ann, of nearly $22m (£14m) last year and paid less than 14 percent in tax - hugely below the income tax percentage of the average working American. Romney's effective tax rate was half that of Barack Obama and two-and-a-half times less that that of his main Republican rival Newt Gingrich.

He also gave nearly $3m to charitable causes and the Mormon Church - which helped reduce his tax rate to a lower band.

During the GOP debate in Tampa, Florida, the former governor of Massachusetts said: "I have nothing to hide. I won't apologise for being successful."

"You'll see my income, how many taxes I've paid, how much I've paid to charity," he said. "I pay all the taxes that are legally required and not a dollar more. I don't think you want someone as the candidate for president who pays more taxes than he owes."

He said his tax bill is "entirely legal and fair" adding, "I'm proud of the fact that I pay a lot of taxes."

The Washington Post was given a preview of the 550-page financial records document, which goes into intricate details of the value of Romney's assets and where they are.

Income tax
Income tax details of the main players of the general election 2012. (Source: Washington Post)

Many pages are devoted to foreign entities in which Romney has invested including Luxembourg, Ireland and the Cayman Islands, all of which promote tax benefits. None of the investments showed much income, however.

Romney's trustee, Brad Malt, emphasised: "These entities are not evading one dime of tax."

Romney released two years of tax returns, which the Democrat Party has said was not enough.

Democratic strategist Paul Begala said: "Romney's father, who ran for president, released 12 years. Why doesn't his son do the same?"